Erwan Saouter

Mercury biotransformations and their potential for remediation of mercury contamination

Bacterially mediated ionic mercury reduction to volatile Hg0 was shown to play an important role in the geochemical cycling of mercury in a contaminated freshwater pond. This process, and the degradation of methylmercury, could be stimulated to reduce the concentration of methylmercury that is available for accumulation by biota. A study testing the utility of this approach is described.

Comparison of Brachionus calyciflorus 2‐d and microtox® chronic 22‐h tests with Daphnia magna 21‐d test for the chronic toxicity assessment of chemicals

The Daphnia magna 21-d test may be required by European authorities as a criterion for the assessment of aquatic chronic toxicity for the notification of new substances. However, this test has several drawbacks. It is labor-intensive, relatively expensive, and requires the breeding of test organisms. The Brachionous calyciflorus 2-d test and Microtoxr̀ chronic 22-h test do not suffer from these disadvantages and could be used as substitutes for the Daphnia 21-d test for screening assays. During this study, the toxicity of 25 chemicals was measured using both the Microtox chronic toxicity and B. calyciflorus 2-d tests, and the no-observed-effect concentrations (NOECs) were compared to the D. magna 21-d test. The Brachionus test was slightly less sensitive than the Daphnia test, but the correlation between the two tests was relatively good (r2 = 0.88). On average, the Microtox chronic test presented the same sensitivity as the Daphnia test, but the results did not correlate as well (r2 = 0.54). The B. calyciflorus 2-d test, and to a lesser extent the Microtox chronic 22-h test, were able to predict the chronic toxicity values of the Daphnia 21-d test. They constitute promising cost-effective tools for chronic toxicity screening.

An evaluation ofmer-specified reduction of ionic mercury as a remedial tool of a mercury-contaminated freshwater pond

SummaryThe potential former-mediated reduction/volatilization of ionic mercury as a tool in the decontamination of a freshwater pond was evaluated using laboratory incubations and a microcosm simulation. In flask assays inoculations with ionic mercury-resistant bacteria (105−107 cells ml−1) isolated from the pond, significantly increased the rate of mercury loss (MANOVA,P≤0.05) relative to uninoculated controls. The effects of cell density, mercuric mercury concentration, addition of nutrients and supplementation with the sulfhydryl reagent β-mercaptoethanol on the rate of mercury loss, were investigated. Inoculation (by 105 cells ml−1) of a flow-through microcosm that simulated the cycling of mercury in the contaminated pond, stimulated by more than 4-fold the formation of volatile elemental mercury. Thus, biological formation of volatile mercury may hold a promise as a remedial tool of contaminated natural waters.

Microbial reduction of ionic mercury for the removal of mercury from contaminated environments.

Mercury contamination of aquatic environments is a major cause of accumulation of methyl mercury by aquatic biota and of the potential risk of toxicosis to consumers of fish and shellfish. Input of mercury to the environment can be prevented by treating industrial wastes before discharge. Nevertheless, numerous examples exist where contamination occurs because of uncontrolled discharge of mercury-laden waters or where problems created in the past persist. Under these circumstances, the removal of mercury is required by law. Several treatments are available for the removal of mercury from waste water. The majority are based on sorption to material rich in sulfhydryl groups.* These treatments are costly and result in mercury-laden wastes that require disposal. An alternative could be a biological treatment based on the microbial reduction of mercury to a volatile form that can be recovered and re~ycled .~ Bacteria with high tolerance to mercurial compounds are found in all natural environments, but they are most abundant in contaminated ones.4 Resistant strains produce an enzyme, mercuric reductase, that reduces ionic mercury [Hg( II)] to elemental mercury (HgO), which is volatile and is partitioned to the air.5 Although methyl mercury (MeHg), rather than Hg(II), is the form of mercury that is accumulated through the food chain: removal of Hg(I1) may reduce MeHg concentrations by elimination of the substrate for the methylation reaction. In the last two years, we have been investigating microbial reduction of Hg(I1) as a tool in the decontamination of a freshwater pond, Reality Lake (RL), in the vicinity of Oak Ridge, Tennessee. Our approach is based on inducing activities of Hg(1I)reducing bacteria in RL by either adding active strains or by stimulating activities of indigenous strains by the addition of n~ t r i en t s .~ These treatments were tested in

IMPROVING SUBSTANCE INFORMATION IN USETOX®, PART 1: DISCUSSION ON DATA AND APPROACHES FOR ESTIMATING FRESHWATER ECOTOXICITY EFFECT FACTORS

The scientific consensus model USEtox® is recommended by the European Commission as the reference model to characterize life cycle chemical emissions in terms of their potential human toxicity and freshwater aquatic ecotoxicity impacts in the context of the International Reference Life Cycle Data System Handbook and the Environmental Footprint pilot phase looking at products (PEF) and organizations (OEF). Consequently, this model has been systematically used within the PEF/OEF pilot phase by 25 European Union industry sectors, which manufacture a wide variety of consumer products. This testing phase has raised some questions regarding the derivation of and the data used for the chemical-specific freshwater ecotoxicity effect factor in USEtox. For calculating the potential freshwater aquatic ecotoxicity impacts, USEtox bases the effect factor on the chronic hazard concentration (HC50) value for a chemical calculated as the arithmetic mean of all logarithmized geometric means of species-specific chronic median lethal (or effect) concentrations (L[E]C50). We investigated the dependency of the USEtox effect factor on the selection of ecotoxicological data source and toxicological endpoints, and we found that both influence the ecotoxicity ranking of chemicals and may hence influence the conclusions of a PEF/OEF study. We furthermore compared the average measure (HC50) with other types of ecotoxicity effect indicators, such as the lowest species EC50 or no-observable-effect concentration, frequently used in regulatory risk assessment, and demonstrated how they may also influence the ecotoxicity ranking of chemicals. We acknowledge that these indicators represent different aspects of a chemicals ecotoxicity potential and discuss their pros and cons for a comparative chemical assessment as performed in life cycle assessment and in particular within the PEF/OEF context. Environ Toxicol Chem 2017;36:3450-3462.

Improving substance information in USEtox®, part 2: Data for estimating fate and ecosystem exposure factors

The scientific consensus model USEtox® has been developed since 2003 under the auspices of the United Nations Environment Programme-Society of Environmental Toxicology and Chemistry Life Cycle Initiative as a harmonized approach for characterizing human and freshwater toxicity in life cycle assessment and other comparative assessment frameworks. Using physicochemical substance properties, USEtox quantifies potential human toxicity and freshwater ecotoxicity impacts by combining environmental fate, exposure, and toxicity effects information, considering multimedia fate and multipathway exposure processes. The main source to obtain substance properties for USEtox 1.01 and 2.0 is the Estimation Program Interface (EPI Suite™) from the US Environmental Protection Agency. However, since the development of the original USEtox substance databases, new chemical regulations have been enforced in Europe, such as the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) and the Plant Protection Products regulations. These regulations require that a chemical risk assessment for humans and the environment is performed before a chemical is placed on the European market. Consequently, additional physicochemical property data and new toxicological endpoints are now available for thousands of chemical substances. The aim of the present study was to explore the extent to which the new available data can be used as input for USEtox-especially for application in environmental footprint studies-and to discuss how this would influence the quantification of fate and exposure factors. Initial results show that the choice of data source and the parameters selected can greatly influence fate and exposure factors, leading to potentially different rankings and relative contributions of substances to overall human toxicity and ecotoxicity impacts. Moreover, it is crucial to discuss the relevance of the exposure factor for freshwater ecotoxicity impacts, particularly for persistent highly adsorbing and bioaccumulating substances. Environ Toxicol Chem 2017;36:3463-3470.

Toward Harmonizing Ecotoxicity Characterization in Life Cycle Impact Assessment

Ecosystem quality is an important area of protection in life cycle impact assessment (LCIA). Chemical pollution has adverse impacts on ecosystems on a global scale. To improve methods for assessing ecosystem impacts, the Life Cycle Initiative hosted by the United Nations Environment Programme established a task force to evaluate the state-of-the-science in modeling chemical exposure of organisms and the resulting ecotoxicological effects for use in LCIA. The outcome of the task force work will be global guidance and harmonization by recommending changes to the existing practice of exposure and effect modeling in ecotoxicity characterization. These changes will reflect the current science and ensure the stability of recommended practice. Recommendations must work within the needs of LCIA in terms of 1) operating on information from any inventory reporting chemical emissions with limited spatiotemporal information, 2) applying best estimates rather than conservative assumptions to ensure unbiased comparison with results for other impact categories, and 3) yielding results that are additive across substances and life cycle stages and that will allow a quantitative expression of damage to the exposed ecosystem. We describe the current framework and discuss research questions identified in a roadmap. Primary research questions relate to the approach toward ecotoxicological effect assessment, the need to clarify the methods scope and interpretation of its results, the need to consider additional environmental compartments and impact pathways, and the relevance of effect metrics other than the currently applied geometric mean of toxicity effect data across species. Because they often dominate ecotoxicity results in LCIA, we give metals a special focus, including consideration of their possible essentiality and changes in environmental bioavailability. We conclude with a summary of key questions along with preliminary recommendations to address them as well as open questions that require additional research efforts. Environ Toxicol Chem 2018;37:2955-2971.

Estimating chemical ecotoxicity in EU ecolabel and in EU product environmental footprint

The EU Commission Ecolabel and the Product and Environmental Footprint (PEF) aim at promoting the development and consumption of greener products. The product aquatic toxicity score from these 2 methods may lead in some circumstances to opposite conclusions. Although this could be interpreted as an inconsistency, the score should not be compared to each other but used in a complementary way. In short, CDV provided a full product formula aquatic toxicity score, even if some chemicals may never reach or persist in freshwater ecosystems. The USEtox® score, by integrating fate and exposure, focuses on the potential toxicity of persistent-water-soluble chemicals at steady state. Since no risk or safety assessment can be conducted with USEtox® nor with the CDV, both are a hazard-based scoring system. This short communication clarifies the difference between approaches underpinning the toxicity scores used in Ecolabel and PEF, providing guidance on how to interpret the results.

Comparison of Brachionus calyciflorus 2-d and Microtox{reg{underscore}sign} chronic 22-H tests with Daphnia magna 21-d test for the chronic toxicity assessment of chemicals

The Daphnia magna 21-d test may be required by European authorities as a criterion for the assessment of aquatic chronic toxicity for the notification of new substances. However, this test has several drawbacks. It is labor-intensive, relatively expensive, and requires the breeding of test organisms. The Brachionous calyciflorus 2-d test and Microtox chronic 22-h test do not suffer from these disadvantages and could be used as substitutes for the Daphnia 21-d test for screening assays. During this study, the toxicity of 25 chemicals was measured using both the microtox chronic toxicity and B. calyciflorus 2-d tests, and the no-observed-effect concentrations (NOECs) were compared to the D. magna 21-d test. The Brachionus test was slightly less sensitive than the Daphnia test, but the correlation between the two tests was relatively good (r{sup 2} = 0.54). The B. calyciflorus 2-d test, and to a lesser extent the Microtox chronic 22-h test, were able to predict the chronic toxicity values of the Daphnia 21-d test. They constitute promising cost-effective tools for chronic toxicity screening.